a. Field of the Invention
This invention relates to an arrangement of acoustic drivers for use in a loudspeaker system. More particularly, the invention is directed to a manifold for coupling multiple acoustic drivers to a single sound-radiating horn.
b. Description of the Prior Art
Acoustic drivers are often used in conjunction with sound-radiating horns in sound applications requiring high acoustic power output (sound volume), such as in theaters, arenas, or for studio and stage monitoring, discotheques and the like. In many sound systems, separate components such as driver/horn assemblies or conventional cone/enclosure loudspeakers are used for sound reproduction across the entire range of audible sound, with different devices covering the bass, midrange and high frequency portions of the audible spectrum.
A particular sound application may require an especially high power output across the spectrum. With respect to the high frequency range, this has been accomplished in the past in at least two different ways. First, it may be possible simply to increase the number of high frequency driver/horn assemblies. This solution results in destructive interference and requires too much space for many applications. Another solution has been to gang two high frequency drivers to the same sound-radiating horn. A number of difficulties arise when attempting to sum acoustic wavefronts from multiple drivers for radiation through a single horn, including standing wave interference and phase cancellation between the ganged drivers. Additionally, the geometry for providing a constantly expanding cross-section for the acoustic path of each driver presents severe limitations on the design of a multiple driver configuration. As a result, this option has been used with some success only in the clustering of two high frequency drivers.
There are several known structures for combining the outputs of multiple drivers. Most of these devices "bend" the output of each of the drivers at an angle less than ninety, and typically, thirty degrees from the driver on-axis direction to the horn on-axis direction in order to direct the sound into the throat of a single horn.
One such device is illustrated in FIG. 1, and is known as a "Y" manifold, this designation being due to its general resemblance to the letter Y. This manifold 100 comprises a main body section 102, in the form a tube, joined to two arm sections 104,106, also tubular in form. The body section 102 is provided with means 103 for attaching the manifold 100 to the throat port of a sound-radiating horn, the mounting means here being illustrated as a flange. Each of the arm sections 104,106 is similarly provided with means 105,107, respectively, for connecting acoustic drivers to the arm sections so that sound from each driver may be directed into an arm section for summation in the body section 102 and subsequent radiation out through the single horn (not shown) coupled to flange 103.
While the "Y" device is somewhat effective for combining the outputs of two high frequency drivers, the general concept is not successfully applied to high frequency systems where more than two drivers are required.
A "double-Y" manifold 200 for combining the output of four acoustic drivers (not shown) is illustrated in FIG. 2, labelled as prior art. This manifold is of similar design and construction to the "Y" manifold 100 of FIG. 1. The "double-Y" manifold has several limitations, the most significant being its useful frequency range. The manifold response in the high frequency range is disturbed by various internal acoustic interference mechanisms to such a degree that use of the "double-Y" manifold is effectively precluded in that range. In this device, each of the drivers is mounted at approximately the same offset angle from the horn on-axis direction, compounding the effect of a wavelength-dependent interference mechanism known as comb filtering. When a driver on-axis direction differs from the the horn throat on-axis direction, the horn response exhibits drop-outs at spaced intervals along the frequency spectrum, with the location of these response drop-outs being related to the angle at which the driver is offset from the horn on-axis direction. A "double-Y" manifold thus cannot be operated in the high frequency range due to the concurrence of drop-outs from each of the four drivers at the same points along the frequency spectrum.
Furthermore, the cluster of drivers mounted to a "double-Y" manifold is bulky and occupies a large space behind the sound-radiating horn.